424 STUDIES IN IMMUNITY. 



full description of the action of citrate. The dissemination of barium 

 sulphate by the citrate does not increase, with a given dose 

 of powder, with the concentration of the citrate. We have found, 

 for example, that an amount of powder contained in eight drops 

 of our barium sulphate solution, when added to 2 c.c. of fluid, 

 is well disseminated if this fluid contains from 0.005 per cent 

 to 0.1 per cent of citrate. Above this concentration the dissemi- 

 nating property of the solution diminishes, so that, in 20 or 30 per 

 cent citrate, barium sulphate sediments almost as rapidly as in 

 distilled water. This disseminating action may also occur with 

 other substances that are insoluble in water, such as clay, tri- 

 calcium phosphate, animal charcoal, and olive oil. 



We have found that this property in sodium citrate is due to its 

 acid radicale. If increasing doses of citric acid (0.0016 per cent to 

 0.05 per cent in our experiments) are added to a given quantity of 

 barium sulphate, distinct dissemination takes place in certain 

 tubes, as indicated by a suspension of the powder. As with sodium 

 citrate, the disseminating property is minimal with certain doses 

 of citric acid and diminishes with stronger doses of it. These 

 facts may be compared with the recent observations of Freund- 

 lich (Zeitschrift fur phys. Chem., LVII, 4). This author found that 

 charcoal (Bliitkohle) remains for a long time in suspension in methyl- 

 amine, dipropylamine, trimethylamine, pyridin, codein and picric 

 acid; he found that this charcoal suspension has an optimum in the 

 moderate concentrations of these substances. Oechsner de 

 Coninck and Azalier * found that barium sulphate is retained in 

 suspension by the chlorhydrate of methylamine, and that even 

 when it is warm no chemical reaction occurs between this organic 

 fluid and the suspension. 



The disseminating action of the citrate is due to the fact that the 

 suspension adsorbs it. We find, indeed, that on treating a weak 

 solution of citrate with barium sulphate, the property of dissemin- 

 ating fresh barium sulphate is removed. And, what is more, if a 

 uniform amount of barium sulphate is added to increasing doses of 

 citrate, the absolute amounts of citrate fixed, increase, whereas 

 the proportion of the citrate adsorbed varies relatively with the 

 initial mass of the salt. 



* Bull, de le Cl. des Sciences Acad. Roy. de Belg., 1907, No. 6. 



